There is a need for a coronary-artery disease screening method not requiring the risk of an arterial catheter. Digital-subtraction radiographs using iodine-K-edge subtraction suffer from low x-ray intensities and require large iodine concentrations precluding non- invasive techniques. Brighter x-ray sources are needed. We propose to conduct an evaluation of metal oxides as characteristic-line x-ray emitters. Two types of devices will be considered: (1) A high-current pulsed x-ray gun with a metal- oxide-coated thin-target window, (2) A commercially available x- ray tube with a modified metal-oxide-coated rotating anode. These sources are expected to produce a useful flux for K-edge dichromography of approximately 50 times greater than that of filtered bremsstrah-lung. We have also developed a computer simulation of iodine-K-edge dichromography which determines the x-ray flux needed from imaging with a particular x-ray-detector system. This simulation together with an estimate of the characteristic-line x-ray production of our sources, indicate that iodine-K-edge dichromography is possible. We will have at our disposal critical research facilities of Varian Associates, the Stanford Linear Accelerator Center, and Adelphi Technology Inc. This includes x-ray detection equipment, x-ray sources, and vapor-deposition facilities. We have developed a digital x-ray- imaging system which is also available for this work. Adelphi Technology Inc. has extensive experience developing advanced x- ray sources for medical, scientific, and industrial applications. A medical diagnostic imaging system based upon the characteristic- line source being developed here promises a moderate-cost non- invasive method for screening atherosclerosis.